Lithium-sulfur Cells Research Articles

Preparation of Biomass-Derived High Specific Surface Area Carbon with Titanium Nitride Nanoparticles for Lithium-Sulfur Batteries

The widespread challenges facing lithium-sulfur batteries, including the low electrical conductivity of sulfur and its species, electrode volume fluctuations during cycling, and the lithium polysulfides shuttle effect, have hindered their commercialization and practical utility [1,2].Our study addresses these issues by incorporating titanium nitride (TiN) nanoparticles onto high specific surface area porous carbon, exploring this composite's potential as both a sulfur cathode host and separator modifier. The synthesis of the carbon/TiN composite involved two key stages: firstly, the in-situ growth of titanium dioxide (TiO2) nanoparticles on the carbon surface utilizing titanium tetrachloride as a precursor; secondly, the conversion of the TiO2 nanoparticles to TiN nanoparticles through carbothermal nitridization (thermal treatment at 1400 ℃ for 4 hours in a nitrogen medium) [3,4].The lithium-sulfur cell employing the prepared C/TiN-25%@S cathode exhibited an initial discharge capacity of 1155 mAh g-1 at 0.2 C, maintaining a capacity exceeding 700 mAh g-1 after 100 cycles. Notably, the lithium-sulfur cell utilizing the C/TiN-25%@S cathode and a C/TiN-modified separator demonstrated enhanced cycling performance, delivering an initial discharge capacity of 1623 mAh g-1 with retention of over 1126 mAh g-1 after 100 charge/discharge cycles at 0.2 C. Acknowledgments This research was funded by the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan (Grant No. AP19677708).

Heterogeneity in Li-S Batteries Resolved through Operando Synchrotron Diffraction Studies

Lithium-Sulfur (Li-S) batteries are promising candidates for electric vehicle applications due to their very high theoretical specific capacity (1670 mAh/g) and the tremendous availability and low cost of elemental sulfur. However, their practical capacity is substantially smaller (~1000 mAh/g) and their cycling performance is hindered by numerous technical challenges caused by issues on both cathode and anode sides of the system. While Li-S cells with extended cycling lifetimes can be built, they are typically only effective when using excess electrolytes and applied pressure, limiting their utility for practical applications. To gain deeper insights into the origin of missing capacity and the capacity fade of Li-S cells, we conducted operando studies on Li-S pouch cell batteries using synchrotron powder diffraction techniques. This approach enabled us to sensitively track the various crystalline phases involved in the cycling of Li-S batteries and to resolve a variety of inhomogeneities within cells that may affect their performance and lifetime.

Li-Ion Intercalating Cathode for Advanced Lithium-Sulfur Batteries

The advancement of lithium-sulfur (Li-S) batteries represents a significant shift in high-energy-density electrochemical storage, offering energy densities far exceeding those of traditional lithium-ion systems. This research contributes to the evolving field of Li-S batteries by proposing a novel strategy to optimize cathode performance, crucial in harnessing their full potential.Li-S batteries are characterized by their unique electrochemical process, which involves converting elemental sulfur to lithium sulfide (Li2S) during discharge via lithium polysulfide intermediates. A traditional challenge in this process is the notorious shuttle effect caused by lithium polysulfide intermediates. These intermediates, highly soluble in standard electrolytes, migrate continuously between the cathode and anode, leading to substantial active material loss, rapid capacity degradation, and reduced coulombic efficiency. Significant advancements have been made by introducing metal compounds with a chemical affinity for lithium polysulfides. However, a persistent challenge remains: the insulating nature of Li2S, which hinders electron transport. Recent strategies aiming to address these issues have focused on electrolytes with enhanced Li2S solubility to promote three-dimensional (3D) Li2S growth and prevent cathode passivation. Yet, the increased reactivity of such electrolytes poses new challenges, highlighting the need for alternative solutions.Our study explores this challenge, utilizing lithiated metal oxides as intercalating cathode materials to control Li2S growth dynamics. This method offers immediate mitigation of side reactions in the implementation of enhanced electrolytes. The scope of our research encompasses the thorough synthesis and characterization of these intercalating oxides, emphasizing their role in control Li2S growth. Additionally, we delve into the electrochemical characterization of these materials, focusing on their lithiation/delithiation kinetics and the consequent impact on Li-S battery performance. These intercalating oxides, capable of incorporating lithium ions within their crystal structure, present a promising path for aligning lithiation with Li2S formation, thereby fostering effective 3D growth. This contrasts with other oxides where asynchronous lithiation results in conventional two-dimensional (2D) Li2S growth, leading to premature discharge termination and suboptimal battery performance.We introduce a mechanism where 3D Li2S growth is driven by enhanced solvation of Li2S, intricately linked to the lithiation behavior of these oxides. By incorporating these optimized intercalating oxides in Li-S cells, we observe notable improvements in discharge capacity and sulfur utilization. This improvement is especially significant under high sulfur loading conditions, which typically exacerbate the polysulfide shuttle effect and pose formidable challenges for Li-S battery efficiency. Our investigation includes a detailed morphological analysis of Li2S deposition on various cathode surfaces. Employing advanced techniques like ex-situ Scanning Electron Microscopy (SEM) and electrodeposition modeling, we discern distinct Li2S growth patterns. These findings reveal that cathodes incorporating specific intercalating oxides exhibit reduced surface passivation due to predominant 3D Li2S growth, as opposed to the 2D growth observed in other oxide substrates. This variation in growth morphology significantly impacts cell performance, particularly under high sulfur loading conditions, where effective management of Li2S formation and polysulfide shuttling is crucial.In conclusion, this research marks a significant step in addressing the fundamental challenges of Li-S batteries. By leveraging the distinct properties of select intercalating oxides, the study not only deepens our understanding of Li2S growth mechanisms but also demonstrates an effective method to enhance Li-S battery performance. This work lays a foundation for future developments in high-energy-density battery technologies and signifies a crucial advancement towards the realization of more efficient and robust Li-S batteries.

High-Performance Lithium-Sulfur Batteries with Atomic V- and Co-Modified Ketjen Black-Sulfur Composite Cathode

Lithium-sulfur (Li-S) batteries are potential alternatives to lithium-ion batteries, which are known to have certain drawbacks. This has drawn special technological attention. Sulfur’s low electrical conductivity, shuttling of the intermediate polysulfides, the slow conversion reaction kinetics of various lithium polysulfides (LiPS), and the major volume change of sulfur in the lithiation reaction are some of the main issues that still need to be resolved before Li-S batteries can be used in practical applications. Additionally, it is likely because there are not enough prognostic models determining energy densities at the cell and pack level based on materials and cell design, most of the articles do not report system-level metrics, specific energy (Wh kg-1), and energy density (Wh L-1).To overcome these problems, atomic vanadium (V) and cobalt (Co) modified ketjen black-sulfur composite (VCKBS) was prepared and used as a cathode in Li-S batteries. The synthesized composite was characterized by various techniques, e.g., XRD, Raman, SEM, HR-TEM, HAADF-STEM, and XPS spectra. The polysulfide adsorption test showed that V had increased the adsorption ability, and cyclic voltammetry displayed the increased catalytic activity resulting from Co, offering a large number of interfacial active sites and ensuring smooth electron transfer. Cycling performance tests showed an initial specific capacity of 1329 mAh g−1, maintained at 1249 mAh g−1 after 100 cycles. Under a higher sulfur loading (2.4 mg cm−2), at 0.2 C, Li-S cells demonstrated an initial specific capacity of 1201 mAh g−1 and retained 985 mAh g−1 after 300 cycles with a low fading rate of 0.059% per cycle. The rate performance tests showed that the prior capacity is nearly recovered, going from 1C back to 0.1C, demonstrating the superiority of the VCKBS material.In addition to the experimental characterization of the Li-S cell performance, energy densities were also predicted by a proposed system-level performance model. The 1st and 100th discharge capacities were used to forecast the system-level specific energies and energy densities. The system-level specific energies and energy densities based on the 100th discharge capacity of VCKBS cathodes had improvements of 1342 and 568%, respectively. This suggests that an easy route to construct the highly stable cathode material may pave the way for the development of highly efficient Li-S batteries. Acknowledgments Hira Fazal acknowledges support from the Türkiye Scholarship/Research Fellowship Program sponsored by the Prime Ministry of Turkey Presidency for Turks Abroad and Related Communities (21PK070917). Damla Eroglu acknowledges support from the Istanbul Development Agency (Award No: TR10/21/YEP/0001). We also thank the National Natural Science Foundation of China (22171180) and the Science and Technology Commission of Shanghai Municipality (20520710400).

Diketopyrrolopyrroles As Performance Enhancing Additives for Lithium-Sulfur Batteries

Although the lithium-ion battery (LIB) has been instrumental in global electrification, more premium applications (such as electrification of aircraft) require capacities and performance beyond the capabilities of traditional LIB chemistries[1]. Lithium-sulfur (Li-S) batteries are a front runner among next generation battery technologies thanks to their very high theoretical capacities (1675 mAh g-1) and impressive gravimetric energy densities (2,700 Wh kg-1) [2,3]. Despite their potential, there are numerous chemical challenges (polysulfide shuttle, dendrite formation etc.) that must be overcome before widespread adoption of the technology [4]. Electrolyte additives have been explored as a means to facilitate the electron transfer reactions that occur within the cell and improve cell capacity and cyclability [5].Diketopyrrolopyrroles (DPPs) are a class of organic π-conjugated compounds that have garnered significant interest in a variety of electrical applications, including solar cells and sensors [6]. The high electrochemical tunability, made possible through the editable organic structure, makes them suitable candidates for redox active electrolyte additives. Here, we explore DPP derivatives as a novel class of electrolyte additive for improving the cell cycling performance of Li-S batteries. A variety of electrochemical and analytical techniques have been utilised to assess the suitability of DPPs as redox active additives, building an understanding of their interactions with active materials in a Li-S cell. Galvanostatic cycling allows us to connect these electrochemical findings to cell cycling performance, where we observe a large enhancement in capacity. We also present an alternative statistical approach to cell data analysis, providing a more concrete method to assessing cycling enhancement than that shown throughout literature. Figure 1. A box plot displaying the discharge capacities at specific cycle numbers for standard (light grey) and DPP (dark grey) cells to provide a statistical comparison.

High-Temperature Lithium-Sulfur Batteries with Commercial Paper-Derived Solid-State Electrolyte

Solid-state lithium-sulfur (Li-S) battery technologies could power future electric mobility due to their potential high energy density. However, the current solid-state Li-S batteries face several challenges, such as high internal impedance at the electrode/electrolyte interfaces, shuttling of lithium polysulfides, and Li dendrite formation. Herein, we introduced a novel Li-rich cellulose-based solid-state electrolyte in combination with sulfurized polyacrylonitrile (SPAN, 36.5 wt.% S) cathode, leading to durable Li-S batteries for high-temperature applications. We utilized SPAN due to its reasonable conductivity, high reversible capacity, and stable cycling performance. The solid-state electrolyte in this study was prepared by infusing Li ions (Li+) into a copper-coordinated cellulosic paper. The infusion of Li+ was carried out by soaking the copper-treated paper in a 1 M LiTFSI in EC0.5DME0.25DOL0.25 solution (where subscripts indicate the volume fraction), followed by complete evaporation of the solvents. Three types of cellulosic paper were explored, from which the commercial copy paper resulted in the highest area-normalized conductance of 24.4 mS cm-2 and Li-ion transference number of 0.76 at 50 °C. At this temperature, the Li-SPAN cells with paper-based electrolyte delivered an initial reversible capacity of 1536 mAh gs -1 at 168 mA gs -1 (0.1C). After high-temperature cycling for 150 cycles at 0.5C, the Li-SPAN cells exhibited an exceptional capacity retention of 82.2% (from 982 to 807 mAh gs -1). The conformability of the paper-based electrolyte ensures good interfacial contact with the SPAN and Li electrodes. As a result, when this solid-state Li-S battery was subjected to fast charging/discharging (1C) at 50 °C, it delivered a reversible capacity of 670 mAh gs -1. In this talk, we will outline the results from our electron microscopy, X-ray diffraction measurements, electrochemical impedance spectroscopy, and cyclic voltammetry studies on Li-S cells to unravel the superior performance of paper-based Li-S batteries at high temperatures. Figure 1

3D printing of customized Li-S microbatteries

Microbatteries serve as essential energy supply components in microelectronic, wearable and implantable devices. Despite recent efforts, developing lithium metal microbatteries with high energy densities and mechanical flexibility in structural design is still challenging, because of the poor interfacial stability and poor processability of lithium foil. Herein, we developed lithium-sulfur (Li-S) microbatteries with customized configurations using 3D printing techniques, which consist of a printable Li anode hosted within a graphene aerogel framework and a printable S cathode based on a carbon nanocages framework, featuring abundant porous structures and large specific surface areas. Consequently, the 3D-printed Li anode achieves over 900 hours of cycling with low overpotentials at an ultrahigh current density of 10 mA cm−2, and the 3D-printed S cathode delivers an ultrahigh capacity of 21.9 mAh cm−2 at the high thickness of 2.3 mm. Furthermore, the 3D-printed Li-S cell delivers an ultrahigh areal energy density of 48.4 mWh cm−2 at a high power density of 3.5 mW cm−2. The application potential of the 3D-printed customized Li-S microbatteries with arbitrary form factors is demonstrated by LED lighting and powering wearable sensor integration system, paving the way for their applications in miniaturized devices.

Incorporation of electronically and ionically conductive additives in high-loading sulfur cathodes in lean-electrolyte lithium–sulfur cells

Low-cost, high-energy-density lithium–sulfur electrochemical batteries have emerged as a promising solution for next-generation energy-storage technologies. To facilitate the practical application of such batteries, it is necessary to address the remaining scientific and engineering challenges, especially those associated with the high-loading sulfur cathode in a lean-electrolyte cell. In this study, we investigate the electrochemical and overall performance of lithium–sulfur cells with a high-loading sulfur cathode. Notably, this cathode is fabricated using a novel hot-pressing method and incorporates electronically and ionically conductive additives, specifically lithium lanthanum titanate (LLTO) and carbon black, respectively. Material analysis reveals the uniform distribution of additives in the cathodes, with the ionically conductive LLTO effectively adsorbing and converting polysulfides and carbon black enhancing the cathode conductivity. Electrochemical analysis of the lean-electrolyte cells shows that the incorporation of LLTO improves cell performance, with enhanced discharge capacity of 715–836 mAh g−1 at C/5–C/10 rates and notable capacity retention after 100 cycles, compared with cathodes without additives or with carbon black. Further investigations demonstrate the superior performance of the cell incorporating LLTO in a LiNO3-free electrolyte, attributable to the promotion of ion transport and polysulfide adsorption by LLTO, resulting in high discharge capacities (846 mAh g−1 at C/10), efficiency (93–99 %), and stability. Overall, this study compares the effects of electronically and ionically conductive additives on cell performance and highlights the effectiveness of the ionically conductive LLTO. The incorporation of such additives offers innovative solutions to the key challenges for the development of high-performance energy-storage devices.

Modeling the dependence of electrolyte design on lithium-sulfur battery performance

Herein, we offer two electrochemical models, a zero-dimensional (0-D) and a one-dimensional (1-D) model, to mechanistically explore the impact of the electrolyte-to-sulfur (E/S) ratio and electrolyte properties on the discharge behavior of a lithium-sulfur (Li-S) cell. The electrochemically active area in both models is defined based on the carbon weight fraction and reference porosity, so the influence of the carbon loading and E/S ratio on the reaction kinetics is included. Mass transfer of the species must be considered to model the reliance of the discharge capacity on the current density. Instead, the 0-D model is more responsive to the influence of the E/S ratio on the discharge capacity. The effect of electrolyte properties can be modeled implicitly through model parameters. The 0-D model is less sensitive to the variance in model parameters than the 1-D model in terms of the predicted capacity.

Ni/Ni4N nanoparticles anchored on 3D necklace-like carbon framework as free-standing bifunctional host for practical Li-S full cells

Inhibiting the shuttle effect, accelerating sulfur redox kinetics and controlling lithium homogeneous deposition are significant to achieve the flexible lithium-sulfur (Li-S) cells with high energy density and safety. In this study, we successfully synthesized a three-dimensional (3D) free-standing necklace-like fabric consisting of heterostructured Ni/Ni4N nanoparticles confined into hollow carbon cages implanted with N-doped carbon nanofibers (Ni/Ni4N@NCC). This unique 3D necklace-like framework and interface electronic structure of Ni/Ni4N@NCC could effectively addresses the challenges associated with both sulfur cathode and lithium anode in Li-S cells. Combine with experimental tests and DFT simulations, Ni/Ni4N@NCC not only strengthened chemical anchoring and accelerated lithium polysulfides conversion, but also induced Li uniform deposition and growth due to its excellent lithiophilicity and low Li diffusion energy barrier. For the anode, the lithium foil coating with Ni/Ni4N@NCC interlayer (denoted as Li-Ni/Ni4N@NCC anode) showed exceptional long-term cycling stability over 1000 h at the high current density of 5 mA cm−2 for high areal capacity of 5 mAh cm−2. The S-Ni/Ni4N@NCC||Li-Ni/Ni4N@NCC cell with sulfur loading (6.8mg cm−2) exhibited high areal capacities of 6.11 mAh cm−2. The synergetic effect of fascinating necklace-like structure and heterogeneous interface offer instruction for the practically viable design of high-performance flexible Li-S full cells.

Lithium cation-doped tungsten oxide as a bidirectional nanocatalyst for lithium-sulfur batteries with high areal capacity

Lithium-sulfur (Li-S) batteries are promising for high energy-storage applications but suffer from sluggish conversion reaction kinetics and substantial lithium sulfide (Li2S) oxidation barrier, especially under high sulfur loadings. Here, we report a Li cation-doped tungsten oxide (LixWOx) electrocatalyst that efficiently accelerates the S↔Li2S interconversion kinetics. The incorporation of Li dopants into WOx cationic vacancies enables bidirectional electrocatalytic activity for both polysulfide reduction and Li2S oxidation, along with enhanced Li+ diffusion. In conjunction with theoretical calculations, it is discovered that the improved electrocatalytic activity originates from the Li dopant-induced geometric and electronic structural optimization of the LixWOx, which promotes the anchoring of sulfur species at favourable adsorption sites while facilitating the charge transfer kinetics. Consequently, Li-S cells with the LixWOx bidirectional electrocatalyst show stable cycling performance and high sulfur utilization under high sulfur loadings. Our approach provides insights into cation engineering as an effective electrocatalyst design strategy for advancing high-performance Li-S batteries.

Green biomass-derived hierarchically porous non-activated carbon from carob waste for high-performance lithium-sulfur batteries

To expedite the development of lithium-sulfur (Li–S) battery technology, it is necessary to address the inherent technological hurdles surrounding sulfur-based cathodes, including mitigating the shuttle effect and enhancing the electrical conductivity of sulfur. The use of biomass-derived carbonaceous materials offers a promising avenue to alleviate these challenges and help reduce the carbon footprint associated with battery technologies. Herein, we report the green synthesis of carob-derived carbonaceous material without additional physical/chemical activation steps, making the process sustainable, affordable, and eco-friendly. The obtained carob-derived carbon (CC) offers a hierarchical micro/meso/macroporous structure with a high surface area of 633 m2 g−1. The electrochemical performance with a sulfur content of 70% (CC@S70) in the composite and a sulfur mass loading of 1 mg cm−2 delivers an initial discharge capacity of 1405 mAh g−1, reducing to 798 mAh g−1 after 260 cycles. Increasing the sulfur content to 90% in the cathode (CC@S90) yields a high capacity in Li–S cells, reaching a discharge capacity of 937 mAh g−1 with a sulfur loading of 2 mg cm−2 at 0.3C (1C = 1675 mA g−1) after 100 cycles. The improved performance can be attributed to the well-preserved interconnected pores within the carbon material, serving as an efficient framework to accommodate high sulfur content.

Quasi-Solid-State Electrolyte Induced by Metallic MoS2 for Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are a promising high-energy-density technology for next-generation energy storage but suffer from an inadequate lifespan. The poor cycle life of Li-S batteries stems from their commonly adopted catholyte-mediated operating mechanism, where the shuttling of dissolved polysulfides results in active material loss on the sulfur cathode and surface corrosion on the lithium anode. Here, we report in situ formation of a quasi-solid-state electrolyte (QSSE) on the metallic 1T phase molybdenum disulfide (MoS2) host that extends the lifetime of Li-S batteries. We find that the metallic 1T phase MoS2 host is able to initiate the ring-opening polymerization of 1,3-dioxolane (DOL), forming an integrated QSSE inside batteries. Nuclear magnetic resonance analysis reveals that the QSSE consists of ∼13% liquid DOL in a solid polymer matrix. The QSSE efficiently mediates sulfur redox reactions through dissolution-conversion chemistry while simultaneously suppressing polysulfide shuttling. Therefore, while ensuring high sulfur utilization, it avoids degradation of both electrodes, as well as the concomitant electrolyte consumption, leading to enhanced cycling stability. Under a practical lean electrolyte condition (electrolyte-to-sulfur ratio = 2 μL mg-1), Li-S pouch cell batteries with the QSSE demonstrate a capacity retention of 80.7% after 200 cycles, much superior to conventional liquid electrolyte cells that fail within 70 cycles. The QSSE also enables Li-S pouch cell batteries to operate across a wider temperature range (5 to 45 °C), together with improved safety under mechanical damage.

1T-rich MoS2 nanosheets anchored on conductive porous carbon as effective polysulfide promoters for lithium–sulfur batteries

The practical applications of lithium-sulfur (Li-S) batteries have severely been hindered by notorious shuttle effect and sluggish redox kinetics of lithium polysulfide intermediates (LiPSs), which bring about rapid capacity degradation, low coulombic efficiency and poor cycling stability. In this work, 1T-rich MoS2 nanosheets are in-situ developed onto the conductive porous carbon matrix (1T-rich MoS2@PC) as efficient polysulfide promotors for high-performance Li-S batteries. The porous carbon skeleton tightly anchors MoS2 nanosheets to prevent their reaggregation and ensures accessible electrical channels, and at the same time provides a favorable confined space that promotes the generation of 1T-rich MoS2 structure. More importantly, the uniformly distributed metallic 1T-rich MoS2 nanosheets not only affords rich sulfphilic sites and high binding energy for immobilizing LiPSs, but also favors rapid electron transfer and LiPSs conversation kinetics, substantially regulating sulfur chemistry in working cells. Consequently, the Li-S cell assembled with 1T-rich MoS2@PC modified separator delivers a remarkable cycling stability with ultralow capacity decay rate of 0.067% over 500 cycles at 1C. Encouragingly, under harsh conditions (high sulfur loading of 4.78 mg cm−2 and low E/S ratio of 8 μL mg−1), a favorable electrochemical performance can still be demonstrated. This study highlights the profitable design of 1T-rich MoS2/carbon based electrocatalyst for suppressing shuttle effect and promoting catalytic conversation of LiPSs, and has the potential to be applied to in other energy storage systems.

Defect-rich porous graphitic phase carbon nitride layer grafted MXene as desolvation promoter for efficient sulfur conversion in extremely harsh conditions

Lithium-sulfur (Li-S) batteries exhibit superior theoretical capacity and energy density but are still hindered by the sluggish redox conversion kinetic of lithium polysulfides arising from the significant desolvation barrier, especially under high current density or low-temperature environments. Herein, a two-dimensional (2D) porous graphitic phase carbon nitride/MXene (CN-MX) heterostructure with intrinsic defects was designed via electrostatic adherence and in-situ thermal polycondensation. In the design, the defect-rich CN with abundant catalytic activity and porous structure could efficiently facilitate the lithium polysulfides capture, the dissociation of solvated lithium-ion (Li+), and fast Li+ diffusion. Concurrently, 2D MXene nanosheets with high electronic conductivity could act as charge transport channels and provide electrochemical active sites for sulfur redox reactions. The Li-S cells with CN-MX heterostructure modified separator demonstrated uncommon rate performance (945 mAh/g at 4.0 C) and satisfactory areal capacity (5.5 mAh cm−2 at 0.2 C). Most remarkably, even at 0 °C, the assembled Li-S batteries performed favorable cycle stability (91.6% capacity retention after 100 cycles at 0.5 C) and outstanding rate performance (695 mAh/g at 2.0 C), and superior high loading performance (5.1 mAh cm−2 at 0.1 C). This work offers exciting new insights to enable Li-S batteries to operate in extreme environments.

Boosting Cathode Activity and Anode Stability of Lithium-Sulfur Batteries with Vigorous Iodic Species Triggered by Nitrate.

Lithium-sulfur (Li-S) battery with a sulfurized polyacrylonitrile cathode is a promising alternative to Li-ion systems. However, the sluggish charge transfer of cathode and accumulation of inactive Li on anode remain persistent challenges. An advanced electrolyte additive with function towards both cathode and anode holds great promise to address these issues. Herein, we present a new strategy to boost sulfur activity and rejuvenate dead Li simultaneously. In the polar electrolyte containing I2-LiNO3 additives, I3 -/IO3 - are triggered significantly by the reaction between NO3 - and I- ions. The I3 -/IO3 - are reactive to insulated Li2S product of cathode and inactive Li on anode, thus accelerating the conversion reaction of sulfur and recovering Li sources back to battery cycling. The in situ/ex situ spectroscopic and morphologic monitoring reveal the crucial role of iodine in promoting Li2S dissociation and inhibiting dendritic Li growth. With the modified electrolyte, the symmetric Li||Li cells deliver a lifespan of 4000 h with an overpotential less than 12 mV at 0.5 mA cm-2. For Li-S cells, 100 % capacity retention up to thousands of cycles and enhanced rate capability are available. This work demonstrates a feasible strategy on electrolyte engineering for practical applications of Li-S batteries.

Illuminating Polysulfide Distribution in Lithium Sulfur Batteries; Tracking Polysulfide Shuttle Using Operando Optical Fluorescence Microscopy.

High-energy-density lithium sulfur (Li-S) batteries suffer heavily from the polysulfide shuttle effect, a result of the dissolution and transport of intermediate polysulfides from the cathode, into the electrolyte, and onto the anode, leading to rapid cell degradation. If this primary mechanism of cell failure is to be overcome, the distribution, dynamics, and degree of polysulfide transport must first be understood in depth. In this work, operando optical fluorescence microscope imaging of optically accessible Li-S cells is shown to enable real-time qualitative visualization of the spatial distribution of lithium polysulfides, both within the electrolyte and porous cathode. Quantitative determinations of spatial concentration are also possible at a low enough concentration. The distribution throughout cycling is monitored, including direct observation of polysulfide shuttling to the anode and consequent dendrite formation. This was enabled through the optimization of a selective fluorescent dye, verified to fluoresce proportionally with concentration of polysulfides within Li-S cells. This ability to directly and conveniently track the spatial distribution of soluble polysulfide intermediates in Li-S battery electrolytes, while the cell operates, has the potential to have a widespread impact across the field, for example, by enabling the influence of a variety of polysulfide mitigation strategies to be assessed and optimized, including in this work the LiNO3 additive.

Constructing honeycomb-structured LaCoO3 as an efficient polysulfide converter on the separator to achieve practical lithium-sulfur batteries

Owing to its remarkable energy density and specific capacity, lithium-sulfur (Li-S) battery has emerged as one of the most promising energy storage devices. Nevertheless, the shuttle effect and the sluggish conversion of polysulfides significantly impede the practical application of Li-S batteries. Hence, a LaCoO3 functional material with a unique honeycomb structure was designed as an efficient polysulfide converter. The honeycomb-structured LaCoO3 not only exhibits strong bonding energy towards polysulfides but also possesses abundant adsorption sites on its surface. The LaCoO3 material also shows excellent catalytic properties to quickly convert the adsorbed and aggregated polysulfides, effectively suppressing the shuttle effect. Moreover, the honeycomb structure of LaCoO3 can facilitate the rapid wetting and infiltration of the electrolyte. Consequently, the Li-S cell with LaCoO3 functionalized separator provides an areal specific capacity of 3.10 mAh cm−2 after 150 cycles under high sulfur loading of 6.52 mg cm−2. Moreover, under practical conditions where the electrolyte content is as low as 7 μL mg−1 and the sulfur loading is 7.96 mg cm−2, the Li-S battery equipped with LaCoO3-separator can still provide an areal specific capacity of 5.93 mAh cm−2 after 50 cycles.

Active sites-rich zeolitic imidazolate framework/MXene heterostructure modified separator with improved Li+ transport for high-performance Li-S batteries

The inevitable shuttling of lithium polysulfides (LiPSs) and poor redox kinetics restrict real-world applications of lithium-sulfur (Li-S) batteries, although they have been paid plentiful attention. Herein, a thin and multifunctional heterostructure (ZIF-L/MXene), consisting of leaf-like zeolitic imidazolate framework sheets (ZIF-L) and two-dimensional layered Ti3C2Tx MXene nanosheets, is developed for modification of polyolefin-based separators. A good combination of the merits of the ZIF-L and MXene can hinder the restacking of MXene nanosheets and achieve a large specific surface area, thus exposing plentiful active sites for adsorption and catalytic reaction of LiPSs. Taking these obviously synergistic effects, the ZIF-L/MXene heterostructure modified separators not only alleviate the shuttling of LiPSs but also promote their kinetics conversion. Furthermore, with an improved electrolyte affinity, the ZIF-L/MXene modified separators can accelerate the transport of Li+. Thus, the modified separator endows a Li-S cell with an admirable discharge capacity of 1371.7 mAh g-1 at 0.2 C and favorable cycling stability, with a slow capacity decay ratio of 0.075% per cycle during 500 cycles. Even under a sulfur loading of ~ 4.1 mg cm-2, the Li-S battery can achieve an excellent capacity of 990.6 mAh g-1 at 0.1 C and maintain an excellent cycling performance. The novel ZIF-L/MXene heterostructure modified separator in this work can provide an alternative strategy for designing thin and light separators for high-performance Li-S batteries, via the enhancement of redox kinetics and reduction of shuttling of the LiPSs.

Understanding the synergistic improving adsorbed and catalytic activity of polysulfide by design of oxygen vacancies and Li+ lithiation/delithiation behavior in Titanium Oxide separator

The commercialization of lithium-sulfur (Li-S) battery is hindered by severe shuttle effect and sluggish electrochemical kinetics, which are induced by the high dissolution of intermediate lithium polysulfides (LiPSs) in cathode side. Here, we describe a strategy towards efficient adsorption and conversion of polysulfides by designing a functional TiO2-based separator. The enhanced overall electrochemical performance of cells is highly related to the synergistic effect of mutually transformational of TiO2 and LixTiO2 and the existence of oxygen vacancies (OVs). During the charging and discharging process of Li-S cell, the in-situ formation of LixTiO2 assigned to lithiation of anatase TiO2 plays a pivotal role in reversible adsorption and desorption of LiPSs. In addition, we also discussed the effect of OVs, which can act as active sites to accelerate electrochemical kinetics and exhibit stronger chemical interaction with LiPSs. The synergy of lithiation and delithiation process of TiO2 with OVs not only offers an effective pathway towards the improvement of LiPSs adsorption and catalytic performance but could also inspire new ideas on developing functional metal oxides modified separator for Li-S battery. We anticipate that this work will provide new avenues for Li-S battery commercialization.